Testacosides A-D, glycoglycerolipids produced by Microbacterium testaceum isolated from Tedania brasiliensis

Marine bacteria living in association with marine sponges have proven to be a reliable source of biologically active secondary metabolites. However, no studies have yet reported natural products from Microbacterium testaceum spp. We herein report the isolation of a M. testaceum strain from the sponge Tedania brasiliensis. Molecular networking analysis of bioactive pre-fractionated extracts from culture media of M. testaceum enabled the discovery of testacosides A-D. Analysis of spectroscopic data and chemical derivatizations allowed the identification of testacosides A-D as glycoglycerolipids bearing a 1-[α-glucopyranosyl-(1 → 3)-(α-mannopyranosyl)]-glycerol moiety connected to 12-methyltetradecanoic acid for testacoside A (1), 14-methylpentadecanoic acid for testacoside B (2), and 14-methylhexadecanoic acid for testacosides C (3) and D (4). The absolute configuration of the monosaccharide residues was determined by 1H-NMR analysis of the respective diastereomeric thiazolidine derivatives. This is the first report of natural products isolated from cultures of M. testaceum. KEY POINTS: • The first report of metabolites produced by Microbacterium testaceum. • 1-[α-Glucopyranosyl-(1 → 3)-(α-mannopyranosyl)]-glycerol lipids isolated and identified. • Microbacterium testaceum strain isolated from the sponge Tedania brasiliensis.

Glycoglycerolipids from the leaves of Perilla frutescens (L.) Britton (Labiatae) and their anti-inflammatory activities in lipopolysaccharide-stimulated RAW264.7 cells

A described monogalactosyldiacylglycerol (MGDG) and two undescribed digalactosyldiacylglycerols (DGDGs) were isolated from the leaves of Perilla frutescens (L.) Britton (Labiatae) by using silica gel column chromatography and semi-preparative high performance liquid chromatography. The elucidation of complete structure of these compounds were conducted by using MS and NMR techniques. The MGDG (7.5% of total lipids) was identified as 1,2-2-O-(9Z,12Z,15E-octadecatrienoyl)-3-O-(β-D-galactopyranosyl)-sn-glycerol. The two DGDGs (2.8% and 1.0% of total lipids, respectively) were identified as 1-O-(9Z,12Z,15Z-octadecatrienoyl)-2-O-(6Z,9Z,12Z-octadecatrienoyl)-3-O-[β-D-galactopyranosyl-(1″→6')-α-D-galactopyranosyl]-sn-glycerol and 1-O- hexadecanoyl -2-O-(9Z,12Z,15Z-octadecatrienoy -l)-3-O-[β-D-galactopyranosyl-(1″→6')-α-D-galactopyranosyl]-sn-glycerol, respectively. All the isolated MGDG and DGDGs were evaluated for their anti-inflammatory activities in lipopolysaccharide (LPS)-stimulated murine macrophages RAW264.7 cells. All of them showed good inhibitory activities and significantly blocked the production of LPS-induced TNF-α, (IL)-1β and IL-6. The above results shed some light on a better understanding of the traditional anti-inflammatory effect of Perilla frutescens and reveal the potential anti-inflammatory constituents.

coli: Tuning phosphatidic acid and UDP-glucose pathways

Glycolipids are target molecules in biotechnology and biomedicine as biosurfactants, biomaterials and bioactive molecules. An engineered E. coli strain for the production of glycoglycerolipids (GGL) used the MG517 glycolipid synthase from M. genitalium for glucosyl transfer from UDPGlc to diacylglycerol acceptor (Mora-Buyé et al., 2012). The intracellular diacylglycerol pool proved to be the limiting factor for GGL production. Here we designed different metabolic engineering strategies to enhance the availability of precursor substrates for the glycolipid synthase by modulating fatty acids, acyl donor and phosphatidic acid biosynthesis. Knockouts of tesA, fadE and fabR genes involved in fatty acids degradation, overexpression of the transcriptional regulator FadR, the acyltransferases PlsB and C, and the pyrophosphatase Cdh for phosphatidic acid biosynthesis, as well as the phosphatase PgpB for conversion to diacylglycerol were explored with the aim of improving GGL titers. Among the different engineered strains, the ΔtesA strain co-expressing MG517 and a fusion PlsCxPgpB protein was the best producer, with a 350% increase of GGL titer compared to the parental strain expressing MG517 alone. Attempts to boost UDPGlc availability by overexpressing the uridyltransferase GalU or knocking out the UDP-sugar diphosphatase encoding gene ushA did not further improve GGL titers. Most of the strains produced GGL containing a variable number of glucosyl units from mono-to tetra-saccharides. Interestingly, the strains co-expressing Cdh showed a shift in the GGL profile towards the diglucosylated lipid (up to 80% of total GGLs) whereas the strains with a fadR knockout presented a higher amount of unsaturated acyl chains. In all cases, GGL production altered the lipidic composition of the E. coli membrane, observing that GGL replace phosphatidylethanolamine to maintain the overall membrane charge balance.